Method of making a light quantity correction filter and method of manufacturing a color cathode ray tube using the light quantity correction filter made by the method

ABSTRACT

A light quantity correction filter that can implement the desired transmittance distribution precisely and easily without complicating an exposure system, a method of making the light quantity correction filter, and a method of manufacturing a color cathode ray tube using the light quantity correction filter are provided. The method of making the light quantity correction filter comprises providing in an evacuated container an evaporation source, a transparent substrate on which material from the evaporation source is to be deposited to form a light quantity correction filter and an evaporation amount distribution controlling sheet that has a plurality of openings and is disposed between the evaporation source and the transparent substrate, evaporating material from the evaporation source for deposition on the transparent substrate, and controlling the amount of evaporated material deposited on the transparent substrate with the distribution controlling sheet to provide a desired transmittance distribution of evaporated material on the transparent substrate.

FIELD OF THE INVENTION

The present invention relates to a light quantity correction filter usedfor manufacturing a color cathode ray tube, and more particularly to alight quantity correction filter that can implement the desiredtransmittance distribution precisely and easily without complicating anexposure system, and a method of making the same.

BACKGROUND OF THE INVENTION

In general, a phosphor dot layer of three colors, that is, blue, green,and red, is regularly formed on the inner surface of the front panel ofa color cathode ray tube by a photographic method. A light absorptionlayer, which is referred to as a black matrix, is formed around thephosphor dots of three colors to improve the contrast. When forming thephosphor layer and the black matrix on the inner surface of the frontpanel, an exposure system for manufacturing a color cathode ray tube isused.

FIG. 8 shows a schematic diagram of an exposure system for manufacturinga color cathode ray tube. As shown in FIG. 8, the exposure systemcomprises a light source portion 9, a correction lens 10, and a lightquantity correction filter 11. Light irradiated from the light sourceportion 9 passes through the correction lens 10 and the light quantitycorrection filter 11 and exposes a phosphor screen on the inner surfaceof a front panel 12. The light quantity correction filter 11 correctsthe light quantity distribution of the light that passed through thecorrection lens 10 from the light source portion 9 to make it uniform onthe inner surface of the front panel 12.

Methods for correcting the light quantity distribution of the lightirradiated from the light source portion by using a light quantitycorrection filter having the above function include providing apredetermined light transmittance distribution by using a light quantitycorrection filter in which a plurality of stripe-shaped shieldingportions are provided and in which the area ratio of the shieldingportions to light transmission portions between the shielding portionsis adjusted by the width of the shielding portions, as disclosed inJapanese Patent Application (Tokko Sho) No. 58-43853. Another method is,for example, to control the light transmittance by using a lightquantity correction filter comprising an evaporated film, as disclosedin Japanese Patent Application (Tokkai Hei) No. 6-103895.

The light quantity correction filter comprising an evaporated film ismanufactured, for example, by using an apparatus as shown in FIG. 9.FIG. 9 shows a schematic diagram of an apparatus for manufacturing alight quantity correction filter according to the prior art. A shieldingsheet (an evaporation pattern) 13 having an opening 14 is providedbetween a transparent substrate 3 and an evaporation source 2. In thisapparatus, the desired transmittance distribution for correction isobtained on the transparent substrate 3 by rotating the shielding sheet13, changing the rotational speed according to the angle, andcontrolling the evaporation amount by the time integration ratio of theopening to the shielding portion.

Recently, in high-definition color monitor display tubes and colorcathode ray tubes for high-definition televisions, reproducibility ofcolors and a white uniformity have been precisely required along with alarge size, a wide angle deflection, and the flatness of the screensurface. Therefore, a complicated highly precise exposure correction isrequired during the process of forming a phosphor screen, especially theprocess of forming a black matrix. Accordingly, the effect of thecollection and divergence of the lens becomes complicated, and atransmittance distribution for performing the corresponding complicatedhighly precise correction is required for a light quantity correctionfilter that controls the size of a back matrix.

With the correction method using the light quantity correction filtercomprising a plurality of stripe-shaped shielding portions according tothe prior art, however, a mechanism for oscillating the light quantitycorrection filter should be provided in the exposure system. Therefore,the structure of the exposure systems, a large number of which are usedin the process of manufacturing color cathode ray tubes, becomescomplicated. With the method of making the light quantity correctionfilter comprising an evaporated film according to the prior art, theevaporation amount is indirectly controlled by the time integrationratio of the opening to the shielding portion that depends on the shapeof the opening, the rotational speed, and the like. Therefore, theattainable transmittance distribution is limited, and the control of thetransmittance distribution is very complicated. Consequently, it is verydifficult to provide the desired black matrix size distribution with atolerance of 5% or less and obtain a sufficient white quality.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light quantitycorrection filter that can implement the desired transmittancedistribution precisely and easily without complicating an exposuresystem, a method of making the light quantity correction filter, and amethod of manufacturing a color cathode ray tube using the lightquantity correction filter.

In order to accomplish the above object, the present invention providesa method of making a light quantity correction filter comprisingproviding in an evacuated container an evaporation source, a transparentsubstrate on which material from the evaporation source is to bedeposited to form a light quantity correction filter and an evaporationamount distribution controlling sheet that has a plurality of openingsand is disposed between the evaporation source and the transparentsubstrate, evaporating material from the evaporation source fordeposition on the transparent substrate, and controlling the amount ofevaporated material deposited on the transparent substrate with thedistribution controlling sheet to provide a desired transmittancedistribution of evaporated material on the transparent substrate.According to the method of making a light quantity correction filter ofthe present invention, a light quantity correction filter having thedesired transmittance distribution can be manufactured precisely andeasily.

It is preferable that the openings in the distribution controlling sheethave a shape of parallel stripes. According to the preferable example,the fine nonuniformity in the transmittance distribution correspondingto the pitch of the openings in the vertical direction can be eliminatedeasily.

It is preferable that the controlling step comprises oscillating atleast one of the evaporation source, the transparent substrate and thedistribution controlling sheet with respect to the others during theevaporation step. According to the preferable example, the finenonuniformity in the transmittance distribution corresponding to thepitch of the openings can be eliminated easily.

It is preferable that the openings in the distribution controlling sheetare formed to have a longitudinal direction component, and the directionof oscillating is substantially perpendicular to the longitudinaldirection of the openings in the distribution controlling sheet.According to the preferable example, the fine nonuniformity in thetransmittance distribution corresponding to the pitch of the openingscan be eliminated more effectively.

It is preferable that the evaporation source is formed in a shape thatis substantially linear or planar. According to the preferable example,the fine nonuniformity in the transmittance distribution correspondingto the pitch of the openings can be eliminated more effectively, and thecontrol of the transmittance can be more simplified in forming the lightquantity correction filter.

It is preferable that the evaporating step comprises sputtering.According to the preferable example, the nonuniformity of theevaporation amount among the evaporation positions is eliminated, andtherefore a light quantity correction filter having the desiredtransmittance distribution can be manufactured precisely and easily.

The present invention provides a method of manufacturing a color cathoderay tube comprising exposing a front panel for a color cathode ray tubeusing a light quantity correction filter produced in accordance with themethod of making a light quantity correction filter as described aboveand including the front panel in a construction of a color cathode raytube. According to the method of manufacturing a color cathode ray tubeof the present invention, the white quality of the color cathode raytube can be improved effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an apparatus for manufacturing a lightquantity correction filter according to a first embodiment of thepresent invention;

FIG. 2 is an enlarged view of the evaporation amount distributioncontrolling sheet of the apparatus for manufacturing a light quantitycorrection filter in FIG. 1;

FIG. 3 is a graph showing the relationship between the distribution ofthe ratio of opening area of the evaporation amount distributioncontrolling sheet and the transmittance of the light quantity correctionfilter;

FIG. 4 shows parameters of the relative equation of the ratio of openingarea of the evaporation amount distribution controlling sheet and thetransmittance of the light quantity correction filter;

FIG. 5 is a graph showing the relationship between the ratio of openingarea of the evaporation amount distribution controlling sheet and thetransmittance of the light quantity correction filter;

FIG. 6 is a graph showing the transmittance distribution on an arbitraryaxis of the light quantity correction filter formed on the transparentsubstrate and the corresponding size of the black matrix on the screensurface in the first embodiment and the prior art;

FIG. 7 is a schematic diagram of an apparatus for manufacturing a lightquantity correction filter according to a second embodiment of thepresent invention;

FIG. 8 is a schematic diagram of an exposure system for manufacturing acolor cathode ray tube; and

FIG. 9 is a schematic diagram of an apparatus for manufacturing a lightquantity correction filter according to the prior art.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention will be described belowwith reference to the drawings.

FIG. 1 shows a schematic diagram of an apparatus for manufacturing alight quantity correction filter according to a first embodiment of thepresent invention. The apparatus for manufacturing a light quantitycorrection filter in this embodiment comprises an evaporation amountdistribution controlling sheet 1, an evaporation source 2, and atransparent substrate 3, which are located in an evacuated bell jar 4.The evaporation amount distribution controlling sheet 1 is substantiallyparallel to the transparent substrate 3 and is formed of a stainlesssteel or the like having a plurality of holes with a pitch of 4 mm. Fora rectagular sheet of stainless steel having a long side of 40 mm and ashort side of 30 mm, for example, about 8 or 9 holes are formed. Theevaporation source 2 comprises a substance that can form asemitransparent film, such as Inconel or chromium, placed on a heaterboard formed of a tungsten sheet, which is heated by charging withelectricity. The transparent substrate 3 is a base material for forminga light quantity correction filter and is formed of an optical glass orthe like. A light quantity correction filter is formed by evaporatingthe metal of the evaporation source 2 on the transparent substrate 3.

The structure of the apparatus for manufacturing a light quantitycorrection filter will be described below in more detail. Theevaporation amount distribution controlling sheet 1 is provided betweenthe evaporation source 2 and the transparent substrate 3. Theevaporation amount distribution controlling sheet is oscillated in adirection substantially perpendicular to the longitudinal direction ofthe openings (the plurality of holes) by a crank 5 connected to a motor6. The hole of the evaporation amount distribution controlling sheet 1that is on the line between the evaporation source 2 and an arbitraryposition in the transparent substrate 3 has a size required to providethe desired transmittance of the transparent substrate 3 at theposition. Molecules evaporated from the evaporation source 2 reach thetransparent substrate 3 through the holes of the evaporation amountdistribution controlling sheet 1 and form a semitransparent film on thetransparent substrate 3. As the size of the holes becomes larger, moreevaporated molecules reach the transparent substrate 3, thus decreasingthe transmittance of the transparent substrate 3. Therefore, thediameter of the openings of the evaporation amount distributioncontrolling sheet 1 is changed according to their positions as describedbelow to control the evaporation amount for obtaining the requiredtransmittance at the desired position in the transparent substrate 3.The transparent substrate 3 on which the semitransparent film is thusformed serves as the light quantity correction filter.

FIG. 2 (a) shows an enlarged view of an evaporation amount distributioncontrolling sheet 1 having slit-shaped openings 8; FIG. 2 (b) shows anenlarged view of an evaporation amount distribution controlling sheet 1having rectangular openings 8; and FIG. 2 (c) shows an enlarged view ofan evaporation amount distribution controlling sheet 1 having circularopenings 8. The shape and location pattern of the openings 8 aredetermined in such a manner that the degree of opening in the verticaldirection in FIGS. 2 (a)-(c) is greater than that in the horizontaldirection in order to obtain opening distribution characteristics inwhich the longitudinal direction of the rectangular openings 8 and thecircular openings 8 is the same as that of the slit-shaped openings 8.

In FIGS. 2 (a)-(c), P and P₁ represent the pitch in the horizontaldirection in FIGS. 2 (a)-(c), P₂ represents the pitch in the verticaldirection, and W and W₁ represent the width (diameter) of the openings8. The rate of opening area is expressed by the equations shown in FIGS.2 (a)-(c). While the three types of opening shapes are illustrated inthis embodiment, the present invention is not limited to these shapes.The same effects as this embodiment can be obtained with openings ofother shapes, for example, a triangular shape, a square shape, ahexagonal shape, and an elliptic shape, by properly distributing theopenings in the evaporation amount distribution controlling sheet 1.

When the shape of the openings 8 is a rectangle, a circle, a triangle,or the like, the evaporation amount distribution controlling sheet 1 hasa higher strength than that having the slit-shaped openings 8.Therefore, such a shape is advantageous for handling the evaporationamount distribution controlling sheet 1, for example, fixing it.However, a shielding portion is present in both the vertical andhorizontal directions. Therefore, it is necessary to determine theconditions for oscillating the evaporation amount distributioncontrolling sheet 1 in view of the shield effect of the shieldingportion with respect to the amount of evaporated metal. Morespecifically, the oscillating should have not only the component in thedirection perpendicular to the longitudinal direction of the openings(the vertical direction in FIGS. 2 (a)-(c)) but also, at least, thecomponent in the longitudinal direction.

When the shape of the openings 8 is a rectangle, a circle, a triangle,or the like, P₁ is about 2 to 4 mm, and P₂ is about 3 to 10 mm, andtherefore the number of the openings 8 is about 30 to 200.

The transmittance of a correction filter is generally lower in thecenter of a panel where the distance between a light source and thepanel is shorter, and therefore the rate of opening area of theevaporation amount distribution controlling sheet 1 should be higher inthe center. Thus, as shown in FIGS. 2 (a)-(c), openings closer to thecenter of the evaporation amount distribution controlling sheet 1 arelarger in principle. However, this does not mean that the largestopening is always provided in the center or that the openings aresymmetrically provided with respect to the central axis.

FIG. 3 is a graph showing the relationship between the rate of openingarea of the evaporation amount distribution controlling sheet 1 and thetransmittance of the light quantity correction filter. In FIG. 3, thehorizontal axis represents the distance from the center of a screen, andthe vertical axis represents the rate of opening area of the evaporationamount distribution controlling sheet 1 and the transmittance of thelight quantity correction filter, provided that the rate of opening areaof the evaporation amount distribution controlling sheet at a positionis indicated at the corresponding position on the light quantitycorrection filter. When the desired transmittance distribution of thelight quantity correction filter is a distribution 15 indicated by □ inFIG. 3, the distribution of the rate of opening area (or the area of theholes) of the evaporation amount distribution controlling sheet 1required to obtain the desired transmittance distribution is adistribution 16 indicated by ♦. This relationship is expressed by thefollowing equation (1) in which the transmittance Tr at an arbitrarypoint F₁ is expressed by the size of the corresponding hole of theevaporation amount distribution controlling sheet 1: $\begin{matrix}{{Tr} = {Tr}_{0}^{\frac{C_{1}}{C_{0}}\frac{{({R_{1}^{2} + L^{2}})}^{\frac{3}{2}}}{L^{3}}}} & (1)\end{matrix}$

FIG. 4 shows the parameters of the relative equation of the rate ofopening area of the evaporation amount distribution controlling sheet 1and the transmittance of the light quantity correction filter, that is,the equation (1). In FIG. 4, the perpendicular line from the evaporationsource 2 to the transparent substrate 3 is called the evaporation centerline, Tr₀ represents the transmittance at the intersection F₀ of thetransparent substrate 3 and the evaporation center line, R₁ representsthe distance between the intersection F₀ and an arbitrary point F₁ onthe transparent substrate 3, L represents the distance between theevaporation source 2 and the transparent substrate 3, L′ represents thedistance between the evaporation amount distribution controlling sheet 1and the transparent substrate 3, C₀ represents the rate of opening area(or the hole area) at the intersection P₀ of the evaporation amountdistribution controlling sheet 1 and the evaporation center line, and C₁represents the rate of opening area (or the hole area) at theintersection P₁ of the evaporation amount distribution controlling sheet1 and the line between the point F₁ on the transparent substrate 3 andthe evaporation source 2.

FIG. 5 is a graph showing the relationship between the rate of openingarea of the evaporation amount distribution controlling sheet 1 and thetransmittance of the filter when L=120 mm, Tr₀=60%, and C₀=30%. Thesolid line represents the relationship when R₁=40 mm, and the brokenline represents the relationship when R₁=80 mm. In FIG. 5, thehorizontal axis represents the rate of opening area C₁ of theevaporation amount distribution controlling sheet 1, and the verticalaxis represents the transmittance Tr at an arbitrary point F₁ on thetransparent substrate 3 (the light quantity correction filter). Due tothe relationship in FIG. 5, the transmittance of the light quantitycorrection filter can be changed by changing the rate of opening area ofthe evaporation amount distribution controlling sheet 1.

FIG. 6 is a graph for comparing the prior art and this embodiment,showing the relationship between the transmittance distribution on anarbitrary axis of the light quantity correction filter formed on thetransparent substrate and the corresponding size of a black matrix on ascreen surface. In FIG. 6, the horizontal axis represents the distance(position) from the center of the screen, and the vertical axisrepresents the transmittance of the light quantity correction filter andthe size of the black matrix, provided that the transmittance of thefilter at a position is indicated at the corresponding position on thescreen. The broken lines represent the desired values, the alternatelong and short dash lines represent the values in the prior art, and thesolid lines represent the values in this embodiment.

As is apparent from FIG. 6, the light quantity correction filteraccording to the prior art cannot be sufficiently adapted to thecomplicated change of the desired value of the transmittancedistribution. Also, the difference between the desired value and actualvalue of the size of the black matrix formed by using this lightquantity correction filter is not 5% or less. On the other hand, thelight quantity correction filter according to this embodiment can besufficiently adapted to the complicated change of the desired value ofthe transmittance distribution, and a transmittance distribution with adifference of ±5% or less with respect to the desired complicated valuescan be obtained. Thus, the desired value of the size of the black matrixformed by using the light quantity correction filter according to thisembodiment can be substantially achieved.

In this embodiment, it is preferable to oscillate one of the evaporationamount distribution controlling sheet 1, the evaporation source 2, andthe transparent substrate 3 with respect to the other two. According tothe preferable example, the fine nonuniformity of the evaporation amountcorresponding to the pitch of the holes (the openings 8) formed in theevaporation amount distribution controlling sheet 1 can be restrained,because the evaporation amount that is finely nonuniform due to portionsthrough which a metal vapor passes, that is, the openings 8, andportions for shielding from the metal vapor, that is, the shieldingportions 7, becomes uniform by oscillating the evaporation amountdistribution controlling sheet 1. In oscillating any of the evaporationamount distribution controlling sheet 1, the evaporation source 2, andthe transparent substrate 3, improved effects can be obtained by settingthe oscillating width to a value equal to the pitch of the openings 8multiplied by an integer, or by oscillating any of them at a constantspeed. Furthermore, it is preferable to oscillate in a directionsubstantially perpendicular to the longitudinal direction of theopenings 8. According to this example, the fine nonuniformity of theevaporation amount corresponding to the pitch of the openings 8 can berestrained effectively, because the oscillating direction issubstantially the same as the direction in which nonuniformity occurs.

While the case where the evaporation source 2 is a dot-shapedevaporation source is described in this embodiment, the presentinvention is not limited to this case. The shape of the evaporationsource may be a line or a plane. When the shape of the evaporationsource is a plane, the control of the transmittance can be moresimplified in forming a light quantity correction filter.

FIG. 7 shows a schematic diagram of an apparatus for manufacturing alight quantity correction filter according to a second embodiment of thepresent invention. The apparatus for manufacturing a light quantitycorrection filter in this embodiment comprises an evaporation amountdistribution controlling sheet 1, an evaporation source 2 b such as achromium cathode, and a transparent substrate 3, which are located in anevacuated bell jar 4. A DC power supply is connected between theevaporation source 2 b and the transparent substrate 3.

In this embodiment, a high voltage is applied to the cathode and theanode (the evaporation source 2 b and the transparent substrate 3) tocause a glow discharge. Due to the sputtering phenomenon involved in thedischarge, a semitransparent film is formed on the transparent substrate3.

The difference between this embodiment and the first embodiment is thatthe semitransparent film is formed on the transparent substrate byvacuum evaporation in the first embodiment, while the semitransparentfilm is formed on the transparent substrate by sputtering in thisembodiment. This embodiment and the first embodiment are basically thesame with respect to other structures. In this embodiment, theevaporation amount distribution controlling sheet 1 has the samestructure as the first embodiment and functions in the same manner (seeFIGS. 2-6).

In the above embodiments, when L′/=p/s/n holds or L′/L is sufficientlylarger than p/s, in which s is the size of the evaporation source, p isthe pitch of the openings formed in the evaporation amount distributioncontrolling sheet 1, and n is an integer of 1 or more, the finenonuniformity corresponding to the pitch of the openings can berestrained more effectively.

While the case where the evaporation amount distribution controllingsheet 1 is oscillated by using the motor 6 and the crank 5 is describedin the above embodiments, the present invention is not limited to thisstructure. The evaporation amount distribution controlling sheet 1 maybe oscillated by other methods, for example, a method using a motor anda cam, a method using a stepping motor and a ball screw, and a methodusing a linear motor.

While the case where Inconel, chromium, or the like, is used as thesubstance evaporated to form a semitransparent film in the aboveembodiments, the present invention is not limited to these substances.Metals such as silver and rhodium and other inorganic substances can beapplied in the same manner, and the same effects can be obtained.

Furthermore, according to the above embodiments, a light quantitycorrection filter that corrects a light quantity distribution duringexposure with a more improved precision than light quantity correctionfilters formed according to the prior art can be obtained. Therefore,when the light quantity correction filter according to the aboveembodiments is used in forming an exposure device for manufacturing acolor cathode ray tube that exposes a front panel for a color cathoderay tube, the white quality of the color cathode ray tube can beimproved effectively. In the practical color cathode ray tube fordisplay that is manufactured by using the light quantity correctionfilter, a white nonuniformity is hardly perceived. This effect isexpressed by a numerical value. With a manufacturing method according tothe prior art, the difference in the illumination distribution on thepanel is about 5 to 15% after the correction during exposure, and awhite nonuniformity can be perceived. With the manufacturing methodaccording to the present invention, the difference in the illuminationdistribution is 5% or less after, the correction, and therefore thewhite quality can be improved. This is because a black matrix sizedistribution with a difference of ±5% or less with respect to thedesired value can be obtained as described above.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limitative, the scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A method of making a light quantity correctionfilter for exposure of a phosphor screen of a color cathode ray tube,comprising: providing in an evacuated container an evaporation source, atransparent substrate having a surface over which an inorganic materialfrom the evaporation source is to be deposited and an evaporation amountdistribution controlling sheet that has a plurality of openings formedso that a rate of opening area increases gradually toward a center ofthe evaporation amount distribution controlling sheet and is disposedbetween the evaporation source and the transparent substrate;evaporating material from the evaporation source for deposition on thesurface of the transparent substrate; and controlling an amount ofevaporated inorganic material deposited on the transparent substratewith the distribution controlling sheet, wherein the controlling stepcomprises oscillating at least one of the evaporation source, thetransparent substrate and the distribution controlling sheet in adirection substantially perpendicular to a longitudinal direction of theopenings with respect to the others during the evaporation step so thatthe amount of inorganic material deposited on the transparent substrate,which is nonuniform, becomes uniform in a vicinity of a boundary betweenthe openings and a shielded portion, and a desired transmittancedistribution is obtained in the transparent substrate.
 2. The method ofclaim 1, wherein the openings in the distribution controlling sheet havea shape of parallel stripes.
 3. The method of claim 1, wherein theopenings in the distribution controlling sheet are formed to have alongitudinal direction component, and the direction of oscillating issubstantially perpendicular to the longitudinal direction of theopenings in the distribution controlling sheet.
 4. The method of claim1, wherein the evaporation source is formed in a shape that issubstantially linear or planar.
 5. The method of claim 1, wherein theevaporating step comprises sputtering.